Therapeutically active substances may be administered by inhalation to the lungs of a patient for producing a local effect therein. Thereby a rapid onset of the effect is obtained using a low dosage of the substance, and systemic side-effects are reduced. Pressurized containers, in which the active substance is dissolved or suspended in a propellant such as a chlorofluorocarbon, are often used.
From such a container a dosage is released via a valve system and inhaled through a mouthpiece. On release of the dosage the particles formed have a high velocity. Furthermore the aerosol droplets generated in the orifice of the mouthpiece are large as they contain residual amounts of propellant. A reduced particle size is obtaind from an increased distance to the patient as the propellant is then more completely evaporated. A reduced velocity and a reduced particle size are desirable in order to obtain a low deposition of substance on the mucous membranes of the oral cavity i.a. Thereby, a greater portion of the particles may follow the air inhaled into the pulmonary system and a better distribution is obtained into the small lumens of the lungs. Local side effects in the oral cavity may also be avoided as they are dependent on a high local concentration of drug substance.
Inhalation of drugs directly from the mouthpiece of a pressurized container requires a coordination between release of the dosage from the container and inspiration by the patient. Some patients have difficulties in performing such coordination.
It has been proposed to provide a pressurized aerosol container with a cylindrical or pear shaped inhalation tube (Moren, F; Int. J. Pharm. 1 (1978) 205-212). Such inhalation tubes may be used to avoid to some extent problems referred to above. However, to be an effective aid to the patient in need of inhalation therapy an inhalation device must be easy to put into operation. Devices in which parts must be assembled before use should be avoided in view of the acute conditions, e.g. asthmatic conditions under which some patients must take their medication. While providing a sufficient space for retardation of the drug particles and for evaporation of the propellant, the inhalation device must be sufficiently small to be carried with the patient. Further the interior of an inhalation device must be protected from contamination with dust. The object of the present invention is to provide an inhalation device fulfilling these requirements.